Mutation Vest(AKAMutation Armor), is a special item for Mutation Mode. When equipped, Soldiers have one-hit protection against the Mutants (The small Nano Armor icon displays and will disappears upon first hit), and as a Mutant, they will have 1000 armor (This works together with normal armor, so a Mutant can have 1100 armor in total). Armor for mutants won't regenerate, but it will come back when the mutants respawn (HM/HMX). This is a very useful item as the soldiers will have more chance to escepe from the Mutants, and the Mutants can live longer to get to the Soldiers.
When becoming the Commando, the Mutant vest can take up an additional 1000 damage (Players still lose 2 HP though), allowing the Commando to survive longer. This protection is useful against normal attack from the mutants, but less efective against Xeno since a 3000 damage attack can still kill a Commando with 2998 HP.